Effects of temperature and moisture on disease and fruit body development of Mycosphaerella pinodes on pea (Pisum sativum)

The effects of temperature (5-30 degrees C) and the duration of moisture on the development of ascochyta blight (Mycosphaerella pinodes) on pea seedlings, grown under controlled conditions, were investigated. The optimum temperature for monocyclic processes was 20 degrees C. At this temperature, pycnidiospores germinated after 2 h, appressoria formed after 6 h and the germ-tube penetrated the leaf cuticle after 8 h. Disease symptoms were evident after 1 day of incubation and the first pycnidia formed after 3 days. Longer wetting periods were required for disease development and pycnidial formation at non-optimal temperatures. Disease severity and the number of pycnidia formed on leaves increased with temperature from 5 to 20 degrees C, then decreased between 20 and 30 degrees C. Polynomial equations were fitted to predict the stages of infection, incubation, latency and disease development as functions of temperature and duration of moisture. These equations allow comparisons of pathogen spread with plant development and could be incorporated into disease development models used for crop management programmes.